The present species is distinctive in having: 1) robust, multi-branched, fasciculate plants; 2) lanceolate to linear-lanceolate leaves with an ovate or oblong, strongly plicate base and keeled acumen; 3) recurved lower margins and strongly and remotely toothed upper margins; 4) oblong-ellipsoid to oblong-cylindric capsules; and 5) mitrate calyptrae that reach to the middle or lower part of the capsule. Ptychomitrium gardneri is very closely related to the European P. polyphyllum, but it differs from the latter by having more robust plants, with broader, more strongly plicate leaf bases and more acutely dentate upper leaf margins. Ptychomitrium gardneri shows some variations in its leaf form and peristome. The leaf bases are generally ovate to broadly ovate, but some are oblong. The length of the leaf upper part is also variable, especially in some Chinese specimens. Some of the Chinese plants have long-linear upper leaf portions, which are similar to those of the P. gardneri var. angustifolium from Japan. The peristome teeth are normally elongate, linear-lanceolate and coarsely papillose. However, some specimens from China have short, lanceolate, and finely papillose peristome teeth. Ptychomitrium gardneri has a disjunctive eastern Asian and western North American distribution. Its total range has been discussed and well illustrated by T. Cao and Vitt (1994).